Lash adjuster

ABSTRACT

In accordance with the present invention, a lash adjuster is provided for minimizing stress on a valve train system in the event of its failure. Specifically, the present invention lash adjuster is for use in a valve train system having a cam for actuating the opening and closing of a valve, where the cam has a select size and shape for determining the velocity or acceleration of the valve&#39;s opening and closing. The present invention lash adjuster generally comprises a housing having a base and a plunger positioned within the housing at a select axial clearance from the base. This clearance is generally sized and shaped such that, in the event of lash adjuster failure, a select maximum velocity or acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Non-provisional patent application, which claimsbenefit to U.S. Provisional Application Ser. No. 61/255,601, entitled“Lash Adjuster,” filed Oct. 28, 2009, the complete disclosure thereofbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to a lash adjuster for use in avalve train system. Specifically, the present invention is directed to alash adjuster that provides a fail-safe condition to avoid damage to avalve exhaust system upon failure of a hydraulic lash adjuster.

As illustrated in FIG. 1 a, it is known in the art relating to internalcombustion engines, such as diesel engines, and namely locomotive dieselengines 101, to actuate two adjacent valves 120 a, 120 b of an enginecylinder 103 by a rotating cam. The cam generally includes a selectshape which determines the timing, lift, velocity, and acceleration ofthe intake and exhaust valve actuation. As shown in FIG. 1 b, in orderto open the exhaust valves 106 a, 106 b the cam shaft 108 rotates untila cam lobe 104 engages a roller 110 located on a rocker arm 112. Oncethe cam lobe 104 engages the rocker arm 112, the rocker arm 112 engagesa valve bridge 114, which causes compression in adjacent springs 116 a,116 b causing the exhaust valves 106 a, 106 b to open.

Generally, valve systems are subject to various types of deflection. Forexample, valve systems may be subject to thermal expansion as the engineheats up and mechanical deflection due to operational loads. If thevalve sterns 120 a, 120 b thermally and mechanically expand andelongate, the valves 106 a, 1066 are unable to fully close. Because thecomponents of the valve system are exposed to a range of temperaturesthroughout the cycle, a lash adjuster is used to provide a means ofself-adjusting the length of the valve stems 120 a, 120 b to facilitateclosure thereof. Lash adjusters provide adjustability so that there iszero clearance at all times between the valve bridge 114 and the valvesterns 120 a, 120 b, thereby allowing the exhaust valves 106 a, b tooperate effectively, even when thermal expansion occurs. Valve systemsmay incorporate two hydraulic lash adjusters 102 a, 102 b, received insockets 122 a, 122 b located at opposite distal ends of the cross-armportion of the valve bridge 114, to engage and directly act upon theends of the valve stems 120 a, 120 b.

FIG. 2 shows a prior art hydraulic lash adjuster 202 in a closedposition where a ball 230 is held against a ball seat 234 in the lashadjuster 202 body by a light spring 238, thereby closing the aperture224 in the base 240 of the housing 236 of the lash adjuster 202.However, when the exhaust valves begin to open, a force is appliedacross the lash adjusters, causing a small amount of oil to escapethrough the diametrical clearance of the lash adjuster 202, situatedbetween the plunger 242 and the sidewall of the housing 236. This forcealso maintains the internal pressure therein and, acting with the ballspring 238, situates the ball 230 against the seat 234 preventing oilfrom flowing out the aperture 224 defined in the base 240 of the housing236. When the exhaust valve is returned to its seat, the force acrossthe lash adjuster 202 is relaxed and the pressure in the cavity 232drops. This allows the plunger 242 to move downward under the influenceof the plunger spring 244, causing the cavity 232 pressure to drop belowthe oil supply pressure and allowing oil flow into the cavity 232through the aperture 224, making up for leakage until the pressureequalizes.

The cavity 232 of the lash adjuster 202 includes an internal axialclearance 260 between the plunger 242 and the base 240 of the housing236. In the prior art lash adjuster 202 of FIG. 2, this internalclearance 260 is about 0.1 inches. When the lash adjuster 202 isproperly functioning, the force across the lash adjuster 202 acts sothat the plunger 242 may only travel axially between about 0.001 inchesand about 0.005 inches. However, when the lash adjuster 202 fails, thelash adjuster 202 is no longer able to effectively trap oil and maintainthe force and pressure that prevents the plunger 242 from traveling thefull length of the internal axial clearance 260. Therefore, when theprior art lash adjuster 202 of FIG. 2 fails, the plunger 242 travelsabout 0.1 inches until it hits the base 240 of the housing 236.

Moreover, when the lash adjuster fails, because there is no internalpressure within the lash adjuster due to the oil escaping through supplychannels—no force is exerted upon the valve to open or close it untilthe plunger makes contact with the base of the housing 236. Therefore,the valve does not begin to open or close until the valve train lifts toabout 0.1 inches. As shown in FIG. 3, when the valve train is lifted toabout 0.1 inches, the cam has already rotated to about 43 degrees (shownat 302). Similarly, when the valve begins to close, the cam is rotatedto an angle of about 150 degrees (shown at 320) and the valve train islifted to about 0.1 inches.

The timing of valve actuation, in part, depends on what point the cam(i.e. cam angle) is engaging the roller at a given point in time.Because of the select shape of the cam, the steepness of the camcorresponds to the velocity of valve opening and closing. When a lashadjuster is working properly, the opening and closing velocities of thevalve gradually increase or decrease, respectively, as the cam rotates.For instance, as illustrated in FIG. 3, with respect to the properlyfunctioning prior art lash adjuster of FIG. 2, when the cam rotates froman angle of about 0 degrees to about 43 degrees (shown at 301), theopening velocity of the valve gradually reaches about 60 inches/sec, atwhich point (shown at 304) the valve is opened to about 0.1 inches.Similarly, when the cam rotates to an angle of about 150 degrees (shownat 322), the valve begins to gradually close at a reducing velocity fromabout −65 inches/sec until the cam is rotated to an angle of about 158.5degrees (shown at 328) and the valve reaches ramp velocity. The valvecontinues to gradually close at a constant velocity until the cam isrotated to an angle of about 180 degrees (330), at which point the valveis closed.

However, when the prior art lash adjuster fails or momentarilymalfunctions, the opening and closing velocities of the valve are nolonger slow and gradual. In the prior art arrangement of FIG. 2, whenthe lash adjuster fails or momentarily malfunctions, the plunger travelsabout 0.1 inches before it contacts the base of the housing 236. Whenthis happens, the valve gear is well beyond the end of the ramp and upthe flank of cam profile before the valve opens (the same is true on theclosing side of the event). As a result, the valve opens and closes atvery high velocities—as much as ten times ramp velocity.

For instance, as shown in FIG. 3, when the prior art lash adjuster ofFIG. 2 fails, instead of having a gradual opening velocity, the velocityof the valve increases instantaneously from about 0 inches/sec (shown at308) to about 60 inches/sec (shown at 316). In this failed condition, asthe cam rotates from about 0 degrees (shown at 300) to about 43 degrees(shown at 306), the velocity of the valve remains at about 0 inches/sec(shown at 308). However, when the cam reaches an angle of about 43degrees, the valve suddenly opens (shown at 316) at a velocity of about60 inches/sec (shown at 304). Similarly, when the prior art lashadjuster of FIG. 2 fails, the closing velocity of the valve is abrupt,instead of gradual. As the cam rotates from about 140 degrees (shown at319) to about 150 degrees (shown at 322), the valve is slowly beginningto close at a gradually increasing negative velocity. However, when theprior art lash adjuster has failed, as the cam reaches an angle of about150 degrees, the valve makes contact with the cylinder head and thevelocity suddenly decreases (shown at 326) to a velocity of 0 inches/sec(shown 324). When the valves open and close at high velocities, thevalves, and other system components, are subjected to high impact loads,which frequently result in valve system failure. Thus, it is an objectof the present invention to provide a lash adjuster with a select axialclearance, between the plunger and housing, that is generally sized andshaped such that, in the event of lash adjuster failure, a selectmaximum velocity of valve opening and closing is maintained, therebyminimizing stress on the valve train system in the event of suchfailure.

Additionally, when the prior art lash adjuster of FIG. 2 fails, theopening and closing accelerations of the valve become abrupt instead ofgradual. As shown in FIG. 4, when a prior art lash adjuster is workingproperly, as the cam rotates from about 0 degrees to about 43 degrees,the opening acceleration of the valve should correspondingly increasegradually from about 0 inches/secinches/sec² to about 27,100 inches/sec²(shown between 400 and 402). However, when the lash adjuster fails, theopening acceleration of the valve increases abruptly from 0 inches/sec²(shown at 408) to about 329,900 inches/sec² (shown at 404). In thisfailed condition, as the cam rotates from about 0 degrees to about 43degrees, the acceleration of the valve remains at about 0 inches/sec²(shown at 406). However, when the cam reaches an angle of about 43degrees (shown at 408), the valve suddenly accelerates at a rate ofabout 329,887.1 inches/sec² (shown at 404).

Similarly, when a prior art lash adjuster is working properly, as thecam rotates from about 150 degrees to about 180 degrees, the closingacceleration of the valve should correspondingly decrease gradually fromabout 30,000 inches/sec² (shown at 412) to 0 inches/sec² (shown at 411).However, when the lash adjuster fails, the closing acceleration of thevalve spikes to 380,900 inches/sec² (shown at 414) and decreasesabruptly to 0 inches/sec² (shown at 418). In this failed condition, asthe cam rotates from about 150 degrees to about 180 degrees, theacceleration of the valve remains at about 0 inches/sec² (shown at 416).When the valves open and close at high acceleration rates, the valves,and other system components, are subjected to high impact loads, whichfrequently results in valve system failure. Thus, it is a further objectof the present invention to provide a lash adjuster with a select axialclearance, that is generally sized and shaped such that, in the event oflash adjuster failure, a select maximum acceleration of valve openingand closing is maintained, thereby minimizing stress on the valve trainsystem in the event of such failure.

SUMMARY OF INVENTION

In accordance with the present invention, a lash adjuster is providedfor minimizing stress on a valve train system in the event of itsfailure. Specifically, the present invention lash adjuster is for use ina valve train system having a cam for actuating the opening and closingof a valve, where the cam has a select size and shape for determiningthe velocity or acceleration of the valve's opening and closing. Thepresent invention lash adjuster generally comprises a housing having abase and a plunger positioned within the housing at a select axialclearance from the base. This axial clearance is generally sized andshaped such that, in the event of lash adjuster failure, a selectmaximum velocity and/or maximum acceleration of valve opening andclosing is maintained, thereby minimizing stress on the valve trainsystem.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and is provided in the contextof a patent application and its requirements. Various modifications tothe preferred embodiment and the generic principles and featuresdescribed herein will be readily apparent to those skilled in the art.Thus, the present invention is not intended to be limited to theembodiments shown, but is to be accorded the widest scope consistentwith the principles and features described herein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a is a cross-sectional view of a prior art locomotive dieselengine, of which the present invention fail-safe lash adjuster is apart.

FIG. 1 b is a cross-sectional view of a prior art valve train system, ofwhich the present invention fail-safe lash adjuster is a part.

FIG. 2 is a cross-sectional view of a prior art lash adjuster.

FIG. 3 is a chart depicting the relationship between cam angle and valveopening and closing velocity of the present invention fail-safe lashadjuster in comparison to prior art lash-adjusters.

FIG. 4 is a chart depicting the relationship between cam angle and valveacceleration of the present invention fail-safe lash adjuster incomparison to prior art lash-adjusters.

FIG. 5 is a cross-sectional view of the present invention fail-safe lashadjuster.

DETAILED DESCRIPTION OF DRAWINGS

In accordance with the present invention, a fail-safe lash adjuster isprovided for minimizing stress on a valve train system in the event ofits failure. The valve train system includes a cam for actuating theopening and closing of at least one valve, where the cam has a selectsize and shape for determining the velocity or acceleration of valveopening and closing. The valve train also includes a member having alash adjuster to maintain zero clearance between at least one valve tipand a member. This member may be in the form of a rocker arm, a valvebridge, or a cam follower. The lash adjuster comprises a housing and aplunger situated within the housing and positioned at a select axialclearance from the base of the housing. This axial clearance is sizedand shaped such that in the event of lash adjuster failure, a selectmaximum velocity and/or acceleration of valve opening and closing ismaintained, thereby minimizing stress on the valve train system.

In one embodiment, shown in FIG. 5 in a closed position, the presentinvention lash adjuster 502 includes a ball 530 that is held against aball seat 534 in the lash adjuster body by a light spring 538, therebyclosing the aperture 524 in the base 540 of the housing 536 of the lashadjuster 502. In this embodiment, when a valve of the valve train systembegins to open, a force is applied across the lash adjuster 502, causinga small amount of oil to escape through the diametrical clearance of thelash adjuster 502, situated between the plunger 542 and the sidewall ofthe housing 536. Additionally, the force applied across the lashadjuster 502 maintains the internal pressure therein and, acting withthe ball spring 538, situates the ball 530 against the seat 534 toprevent oil from flowing out the aperture 524 defined in the base 540 ofthe housing 536. When the exhaust valve is returned to its seat, theforce across the lash adjuster 502 is relaxed and the pressure in thecavity 532 drops. This allows the plunger 542 to move downward under theinfluence of the plunger spring 544, causing the cavity 532 pressure todrop below the oil supply pressure and allowing oil flow into the cavity532 through the aperture 524 until the pressure equalizes.

Like the prior art lash adjuster of FIG. 2, when the present inventionlash adjuster 502 of FIG. 5 is properly functioning, the force acrossthe lash adjuster 502 acts so that the plunger 542 may only travelaxially between about 0.001 inches and about 0.005 inches. Moreover,like the prior art lash adjuster, when the present invention lashadjuster 502 fails, it is no longer able to effectively trap oil andmaintain the force and pressure that keeps the plunger 542 fromtraveling the full length of the internal axial clearance 560. Moreover,when the lash adjuster fails, because there is no internal pressurewithin the lash adjuster—due to the oil escaping through the supplychannels—no force is exerted upon the valve to open or close it untilthe plunger makes contact with the base of the housing 536.

As shown in FIG. 5, the internal axial clearance 560 of the presentinvention lash adjuster 502 is selected at a length of about 0.01 inchesto about 0.03 inches, and preferably about 0.02 inches. Therefore, in afailed condition, the valve will begin to open or close when the valvetrain is lifted between about 0.01 inches and about 0.03 inches, andpreferably about 0.02 inches. Moreover, as a result of this decreasedinternal axial clearance 560, in the event of failure, the presentinvention lash adjuster 502 may be set at the minimum velocity andtravel an axial distance of between about 0.01 inches and about 0.03inches (preferably about 0.02 inches) within the lash adjuster 502 body.Thus, when the lash adjuster 502 fails or momentarily malfunctions, theplunger 542 only travels between about 0.01 inches to about 0.03 inches,and preferably about 0.02 inches, before it contacts the base 540 of thehousing 536, causing the valve to open.

When the valve opens between about 0.01 to about 0.03 inches, andpreferably about 0.02 inches, there is less damage to the valve trainsystem in the event of failure than when the valve opens about 0.1inches (as in the prior art lash adjuster arrangement of FIG. 2). Valveactuation depends on what point the cam is engaging the roller at agiven point in time. Thus, the cam angle determines the valve trainlift. Additionally, because of the select shape of the cam, thesteepness of the cam corresponds to velocity and acceleration of valveopening and closing. Because cam angle also corresponds to valvevelocity and acceleration, there is a correlation between valve trainlift and valve velocity and acceleration. Thus, the lower the valvetrain lift when the valve opens or closes, the lower the opening andclosing valve velocity will be. The lower the opening and/or closingvelocity, the less damage there is to the valve train system.

For instance, as shown in FIG. 3, when the valve train is lifted toabout 0.03 inches when the valve opens (when the present invention lashadjuster is functioning properly), the cam rotates from about 0 degrees(shown at 310) to about 32.5 degrees (shown at 312), and the valveopening velocity gradually increases from about 0 inches/sec (shown at300) to about 14.44 inches/sec (shown at 314). Similarly, when the valvetrain is lifted to about 0.03 inches when the valve closes (when thepresent invention lash adjuster is functioning properly), the earnrotates from about 158 degrees (shown at 332) to about 180 degrees(shown at 311), and the valve closing velocity gradually increases fromabout −20 inches/sec (shown at 328) to 0 inches/sec (shown at 330).

In a valve train system with a properly functioning lash adjuster, theincrease in valve opening and closing velocities is gradual. However,unlike the prior art lash adjuster, if the present invention lashadjuster fails, the change in opening velocity (shown at 303) andclosing velocity (shown at 315) of the valve remains more gradual. Forinstance, in a valve train system having a failed present invention lashadjuster, as the cam rotates from about 0 degrees (shown at 300) toabout 32.5 degrees (shown at 317), the velocity of the valve remainsabout 0 inches/sec (shown at 303). When the cam reaches an angle ofabout 32.5 degrees (shown at 317), the valve opens at a velocity of onlyabout 14.40 inches/sec (shown between 317 and 314). However, thisincrease in velocity is not significantly different from the gradualincrease in velocity when the lash adjuster is working properly. Thechange in velocity remains relatively gradual. As a result, the valvegear is still on the ramp when the valve opens. Therefore, there islimited stress on the system and damage to the valve train is avoided.

Similarly, in a valve train system having a failed present inventionlash adjuster, the valve gradually closes until the cam is rotated to anangle of about 158.5 degrees, when the valve train is lifted about 0.03inches. When the cam reaches an angle of about 158.5 degrees, the valvecloses at a velocity of only about −20 inches/see. As the cam rotatesfrom about 158.5 degrees (328) to about 0 degrees (330), the velocity ofthe valves remains about 0 inches/sec (shown at 315). However, thisincrease in velocity is not significantly different from the gradualincrease in velocity when the lash adjuster is working properly. Thechange in velocity remains relatively gradual. As a result, the valvegear is still on the ramp when the valve closes. Therefore, there islimited stress on the system and damage to the valve train is avoided.

Additionally, in a valve train system having a failed present inventionlash adjuster, the opening and closing valve accelerations remainsimilar to the opening and closing valve accelerations when the lashadjuster is working properly. In contrast to the rapid acceleration ratethat the prior art lash adjuster's failure causes the valve to open at,the valve opening acceleration rate in a system having a failed presentinvention lash adjuster is relatively small and gradual. As shown inFIG. 4, when the present invention lash adjuster is working properly, asthe cam rotates from about 0 degrees to about 32.5 degrees, the openingacceleration of the valve correspondingly increases at gradual rate fromabout 0 inches/sec² (shown at 400) to about 16,00 inches/sec² (shown at405). In contrast to a failed prior art lash adjuster, which causes thevalve opening acceleration to increase abruptly from about 0 inches/sec²to about 329,900 inches/sec² (shown at 404), a failed present inventionlash adjuster only causes the valve opening acceleration to increasefrom about 0 inches/sec² (shown at 400) to about 78,000 inches/sec²(shown at 410). Thus, the opening acceleration rate of a failed presentinvention lash adjuster is not significantly different from theacceleration rate when the lash adjuster is properly functioning.Similarly, the closing acceleration rate of a failed present inventionlash adjuster is not significantly different from that when it isworking properly. The valve closing acceleration rate in a system havinga failed present invention lash adjuster decreases from about 107,700inches/sec² (shown at 417) to about 0 inches/sec² (shown at 420), incontrast to decreasing from 19,900 inches/sec² (shown at 419) to about 0inches/sec² when it is functioning properly. As a result, the presentinvention lash adjuster minimizes stress on the valve train system inthe event of such failure, thereby avoiding damage.

Lash adjuster failure may involve the failure or malfunction of one ormore parts of the lash adjuster, such as the ball retainer, the ballspring, or the engagement between the ball and seat.

1. A lash adjuster for use in a valve train system, said valve trainsystem having a cam for actuating the opening and closing of at leastone valve, wherein said cam has a select size and shape for determiningthe velocity of valve opening and closing, a member having a lashadjuster to maintain zero clearance between at least one valve tip andsaid member, said lash adjuster comprising, a housing having a base, aplunger situated within said housing and being situated at a selectaxial clearance from the base of said housing, wherein the select axialclearance is sized and shaped such that in the event of lash adjusterfailure, a select maximum velocity of valve opening and closing ismaintained, thereby minimizing stress on the valve train system in theevent of lash adjuster failure.
 2. The lash adjuster of claim 1 whereinsaid member is a rocker arm.
 3. The lash adjuster of claim 1 whereinsaid member is a valve bridge.
 4. The lash adjuster of claim 1 whereinsaid member is a cam.
 5. The lash adjuster of claim 1 further comprisinga ball retainer for retaining a ball near the base of said housing. 6.The lash adjuster of claim 5, wherein failure of said ball retainerresults in lash adjuster failure.
 7. The lash adjuster of claim 5further comprising a ball spring for holding said ball against a seat inthe base of said housing.
 8. The lash adjuster of claim 7, whereinfailure of said spring results in lash adjuster failure.
 9. The lashadjuster of claim 7, wherein malfunction of the engagement between saidball and seat results in lash adjuster failure.
 10. The lash adjuster ofclaim 1, wherein the select axial clearance is sized to have a length ofbetween about 0.01 inches and about 0.03 inches.
 11. The lash adjusterof claim 1, wherein the select axial clearance is sized to have a lengthof about 0.02 inches.
 12. The lash adjuster of claim 1, wherein themaximum velocity of valve opening is between about 5 inches per secondand about 14.40 inches per second and the maximum velocity of valveclosing is between about 15 inches per second and about 20 inches persecond.
 13. The lash adjuster of claim 1, wherein the change in openingand closing velocities of the valve remain relatively gradual.
 14. Alash adjuster for use in a valve train system, said valve train systemhaving a cam for actuating opening and closing of at least one valve,wherein said cam has a select size and shape for determining theacceleration of valve opening and closing, a member having a lashadjuster to maintain zero clearance between at least one valve tip andmember, said lash adjuster comprising, a housing having a base, aplunger situated within said housing and being situated at a selectaxial clearance from the base of said housing, wherein the select axialclearance is sized and shaped such that in the event of lash adjusterfailure, a select maximum acceleration of valve opening and closing ismaintained, thereby minimizing stress on the valve train system in theevent of lash adjuster failure.
 15. The lash adjuster of claim 14wherein said member is a rocker arm.
 16. The lash adjuster of claim 14wherein said member is a valve bridge.
 17. The lash adjuster of claim 14wherein said member is a cam.
 18. The lash adjuster of claim 14 furthercomprising a ball retainer for retaining a ball near the base of saidhousing.
 19. The lash adjuster of claim 18, wherein failure of said ballretainer results in lash adjuster failure.
 20. The lash adjuster ofclaim 18 further comprising a ball spring for holding said ball againsta seat in the base of said housing.
 21. The lash adjuster of claim 20,wherein failure of said spring results in lash adjuster failure.
 22. Thelash adjuster of claim 20, wherein malfunction of the engagement betweensaid ball and seat results in lash adjuster failure.
 23. The lashadjuster of claim 14, wherein the axial clearance is sized to have alength of between about 0.01 inches and about 0.03 inches.
 24. The lashadjuster of claim 14, wherein the axial clearance is sized to have alength of about 0.025 inches.
 25. The lash adjuster of claim 18, whereinthe maximum acceleration of valve opening is about 78,000 inches/second²and the maximum acceleration of valve closing is about 107,700inches/second².